7 research outputs found
Regulation of autophagy by Gigaxonin-E3 ligase, and its involvement in neurodegenerative diseases
L'autophagie est l'une des voies de signalisation qui maintiennent l'homĂ©ostasie cellulaire en condition basale, mais aussi en rĂ©ponse Ă un stress. Son rĂŽle est essentiel pour assurer plusieurs fonctions physiologiques, et son altĂ©ration est associĂ©e Ă de nombreuses maladies, parmi lesquelles le cancer, les maladies immunitaires et les maladies neurodĂ©gĂ©nĂ©ratives. Un nombre croissant d'Ă©tudes a Ă©tabli que la voie autophagique est finement contrĂŽlĂ©e. Cependant, trĂšs peu est connu sur les mĂ©canismes molĂ©culaires assurant sa rĂ©gulation mais la famille des E3-ligases joue un rĂŽle primordiale. La Gigaxonine est un adaptateur de la famille des E3 ligases CUL3, qui spĂ©cifie les substrats pour leur ubiquitination et leur successive dĂ©gradation. Des mutations «perte de fonction» de la Gigaxonine causent la Neuropathie Ă Axones GĂ©ants (NAG), une maladie neurodĂ©gĂ©nĂ©rative sĂ©vĂšre et fatale, qui impacte tout le systĂšme nerveux et provoque une agrĂ©gation anormale des Filaments IntermĂ©diaires (FI) dans l'organisme entier. GrĂące Ă la modĂ©lisation de la pathologie dans les cellules de patients et chez la souris, le laboratoire a pu mettre en avant le rĂŽle crucial de la Gigaxonine dans la dĂ©gradation de la famille des FIs, Ă travers son activitĂ© d'ubiquitination.Au cours de ma thĂšse, j'ai Ă©tudiĂ© les mĂ©canismes de neurodĂ©gĂ©nerescence de la NAG, et la possible altĂ©ration de la voie autophagique.Pour cela, j'ai dĂ©veloppĂ© un nouveau modĂšle neuronal de la maladie, Ă partir de notre modĂšle murin NAG, qui reproduit la mort neuronale et l'agrĂ©gation des FIs retrouvĂ©es chez les patients. Pour Ă©tudier l'implication de l'autophagie dans la neurodĂ©gĂ©nĂ©rescence, j'ai Ă©valuĂ© l'effet de la dĂ©plĂ©tion de la Gigaxonine sur la formation des autophagosomes, le flux autophagique, la fusion avec le lysosome et la dĂ©gradation. Jâai ainsi rĂ©vĂ©lĂ© un dĂ©faut dans la dynamique autophagique dans les neurones NAG -/-. Pour dĂ©chiffrer les mĂ©canismes molĂ©culaires sous-jacents, j'ai Ă©tudiĂ© l'effet de l'absence de la Gigaxonine sur diffĂ©rentes rĂ©gulateurs de la voie. En utilisant des techniques complĂ©mentaires, j'ai montrĂ© que la Gigaxonine est essentielle pour le turn-over dâun interrupteur autophagique, Ă travers son activitĂ© dâE3-ligase.En conclusion, nous avons identifiĂ© un nouveau mĂ©canisme molĂ©culaire impliquĂ© dans le contrĂŽle des premiĂšres phases de l'autophagie. Non seulement ces rĂ©sultats prĂ©sentent une avancĂ©e significative dans le domaine de l'autophagie, ils contribuent Ă©galement Ă la comprĂ©hension de son dysfonctionnement dans les maladies neurodĂ©gĂ©nĂ©ratives, et pourraient gĂ©nĂ©rer une nouvelle cible pour une intervention thĂ©rapeutique chez l'homme.The autophagic route is one of the signaling pathways that sustain cellular homeostasis in basal condition, but also in response to stress. It has been shown to be crucial for several physiological functions and its impairment is associated with many diseases, including cancer, immune and neurodegenerative diseases. While an expanding number of studies have shown that autophagic route is finely controlled, little is known about the molecular mechanisms ensuring its function, but a fundamental role is sustained by the family of E3 ligases. Gigaxonin is an adaptor of a Cul3-E3 ligase, which specifies the substrates for their ubiquitination and their subsequent degradation. âLoss of functionâ mutations in Gigaxonin cause Giant Axonal Neuropathy (GAN), a severe and fatal neurodegenerative disorder that impacts broadly the nervous system and cause an abnormal aggregation of Intermediate Filaments (IFs) through the body. Modeling the disease in patientâs cells and in mouse, the laboratory has demonstrated the crucial role of Gigaxonin in degrading the entire family of IFs through its ubiquitination activity.During my PhD, I studied the neurodegenerative mechanisms in GAN disease, and the possible impairment of autophagy pathway.For that purpose, I developed a new neuronal model of the disease from our GAN mouse, which reproduced the neurodegeneration and the IF aggregation found in patients. To investigate the involvement of autophagy in neurodegeneration, I evaluated the effect of Gigaxonin depletion on autophagosome formation, autophagic flux, lysosome fusion and degradation, and I revealed a defect in autophagy dynamics. To decipher the molecular mechanism of autophagosome impairment, I investigated the effect of Gigaxonin depletion on different autophagy regulators. Using complementary techniques, I showed that Gigaxonin is essential for the turn-over of a specific molecular switch, through its E3 ligase activity.Altogether, we identified a new exciting molecular mechanism in the control of autophagy. Not only these findings present a significant advance in the comprehension of the fundamental field of autophagy, but it also contribute in the understanding of its dysfunction in neurodegenerative diseases, and may generate a new target for therapeutic intervention in humans
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The different autophagy degradation pathways and neurodegeneration.
The term autophagy encompasses different pathways that route cytoplasmic material to lysosomes for degradation and includes macroautophagy, chaperone-mediated autophagy, and microautophagy. Since these pathways are crucial for degradation of aggregate-prone proteins and dysfunctional organelles such as mitochondria, they help to maintain cellular homeostasis. As post-mitotic neurons cannot dilute unwanted protein and organelle accumulation by cell division, the nervous system is particularly dependent on autophagic pathways. This dependence may be a vulnerability as people age and these processes become less effective in the brain. Here, we will review how the different autophagic pathways may protect against neurodegeneration, giving examples of both polygenic and monogenic diseases. We have considered how autophagy may have roles in normal CNS functions and the relationships between these degradative pathways and different types of programmed cell death. Finally, we will provide an overview of recently described strategies for upregulating autophagic pathways for therapeutic purposes.This work was supported by UK Dementia Research Institute (funded by the MRC, Alzheimer's Research UK and the Alzheimer's Society), Alzheimer's Research UK (ARUK-2022DDI-CAM, ARUK-TC2020-1 and ARUK-PG2018C-001), The Tau Consortium, Cambridge Centre for Parkinson-Plus, the National Institutes of Health grants AG054108, AG031782, AG021904, NS100717 and the generous support of the Rainwater Charitable Foundation, The JPB Foundation, The Backus Foundation, The Glenn Foundation and R&R Belfer and the NIHR Cambridge Biomedical Research Centre (BRC-1215-20014). The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care'. AMS is supported by a Ramon Areces postdoctoral fellowship and GJK by a T32 GM007491 and a T32 GM007288. MB is supported by an âAllocation Jeune Chercheurâ from Fondation Alzheimer (France)
TSC1 loss increases risk for tauopathy by inducing tau acetylation and preventing tau clearance via chaperone-mediated autophagy.
Age-associated neurodegenerative disorders demonstrating tau-laden intracellular inclusions are known as tauopathies. We previously linked a loss-of-function mutation in the TSC1 gene to tau accumulation and frontotemporal lobar degeneration. Now, we have identified genetic variants in TSC1 that decrease TSC1/hamartin levels and predispose to tauopathies such as Alzheimerâs disease and progressive supranuclear palsy. Cellular and murine models of TSC1 haploinsufficiency, as well as human brains carrying a TSC1 risk variant, accumulated tau protein that exhibited aberrant acetylation. This acetylation hindered tau degradation via chaperone-mediated autophagy, thereby leading to its accumulation. Aberrant tau acetylation in TSC1 haploinsufficiency resulted from the dysregulation of both p300 acetyltransferase and SIRT1 deacetylase. Pharmacological modulation of either enzyme restored tau levels. This study substantiates TSC1 as a novel tauopathy risk gene and includes TSC1 haploinsufficiency as a genetic model for tauopathies. In addition, these findings promote tau acetylation as a rational target for tauopathy therapeutics and diagnostic
Biallelic Variants in UBA5 Reveal that Disruption of the UFM1 Cascade Can Result in Early-Onset Encephalopathy
International audienceVia whole-exome sequencing, we identified rare autosomal-recessive variants in UBA5 in five children from four unrelated families affected with a similar pattern of severe intellectual deficiency, microcephaly, movement disorders, and/or early-onset intractable epilepsy. UBA5 encodes the E1-activating enzyme of ubiquitin-fold modifier 1 (UFM1), a recently identified ubiquitin-like protein. Biochemical studies of mutant UBA5 proteins and studies in fibroblasts from affected individuals revealed that UBA5 mutations impair the process of ufmylation, resulting in an abnormal endoplasmic reticulum structure. In Caenorhabditis elegans, knockout of uba-5 and of human orthologous genes in the UFM1 cascade alter cholinergic, but not glutamatergic, neurotransmission. In addition, uba5 silencing in zebrafish decreased motility while inducing abnormal movements suggestive of seizures. These clinical, biochemical, and experimental findings support our finding of UBA5 mutations as a pathophysiological cause for early-onset encephalopathies due to abnormal protein ufmylation
Biallelic Variants in UBA5 Reveal that Disruption of the UFM1 Cascade Can Result in Early-Onset Encephalopathy
Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)
In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field